ActionScript for Flash MX: The Definitive Guide, 2nd Edition By Colin Moock
Chapter 18. ActionScript Language Reference
Button.onPress( ) Event Handler
Flash 6; on (press) supported since Flash 2
occurs when the mouse button is clicked while the pointer is over a Flash button
theButton.onPress() on (press) { statements }
Description
The onPress( ) event handler executes when the primary mouse button is depressed while the mouse pointer is in the button's hit area. Other mouse buttons (right, middle, scroll, etc.) are not detectable. Note that a "mouseclick" is a two-step process: the mouse button is depressed (press) and then released (release). Button press events are appropriate for radio buttons or weapons firing in a game, but use release events to allow the user to change his mind before releasing the mouse.